Report on the 2016 Pacific Northwest Wetland Condition Assessment

The United States Environmental Agency (USEPA), in partnership with the States and Tribes, performed the first National Wetland Condition Assessment (NWCA) in 2011 and reported that most of the wetland area in the US was in good or fair condition, except for the West Ecoregion, where wetland area was predominantly in poor condition. These results prompted USEPA Region 10 personnel to consult with the Wetlands Team of the Office of Research and Development’s Pacific Ecological Systems Division in Corvallis, Oregon. This led to Region 10 obtaining funding from the USEPA Office of Water through the Regional Applied Research Program to do increased sampling in the PNW in the 2016 NWCA.  The purpose of the 2016 Pacific Northwest Wetland Condition Assessment (PNWCA) was to provide a detailed assessment of biological condition within the Xeric and Western Mountains ecoregions of the PNW, and to compare condition within ecoregions.  The results of the 2016 PNWCA indicate that most of the wetland resource in the PNW (about 84%) is in overall poor condition.  The PNW Western Mountains had more wetland area in good or fair condition (42%) than did the PNW Xeric ecoregion, where about 97% of the resource was in poor condition. The PNWCA determined that the poor wetland condition was largely due to the presence of Nonnative Plants.   Six physical stressors were evaluated -- Vegetation Removal, Vegetation Replacement, Water Addition/Subtraction, Flow Obstruction, Soil Hardening, and Surface Modification.  Most of the PNW wetland area was in good or fair condition relative to these stressors, indicating a low or moderate extent of the stressors.  The patterns of condition with respect to the physical stressors was generally similar between the wetland areas in the PNW and the corresponding non-PNW wetland areas. A risk analysis was performed to determine the influence of the stressors on poor wetland condition and to identify potential management strategies. Poor wetland condition was most likely to be associated with high levels of Vegetation Replacement and Soil Hardening. Removal of any of the stressors except for Flow Obstruction was associated with wetland condition improvement.  Vegetation Replacement had the strongest association; Soil Hardening the second strongest association.  The patterns of risk differ by state within the PNW, and for the Inland Woody and Inland Herbaceous Wetlands. The differences in wetland condition between the ecoregions indicates that, where possible, both the Western Mountains and Xeric ecoregions should be sampled at a sufficient intensity to allow separate evaluations of the ecoregions.

Impact/Purpose

The impetus for the creation of the 2016 Pacific Northwest Wetland Condition Assessment (PNWCA) came from questions asked by resource managers primarily from the Pacific Northwest (PNW), and by USEPA Regional scientists regarding some of the results from the 2011 NWCA.  The response was to obtain additional funding to increase the number of sites sampled so that differences in the condition of wetland area were more likely to be detected in the 2016 NWCA.  Specifically, Region 10 requested and obtained funds through the Office of Research and Development’s Regional Applied Research Program and from the USEPA Office of Water to support an intensified level-of-effort in the PNW during the 2016 NWCA.  The NARS Team at the Pacific Ecological Systems Division in Corvallis, OR, provided technical support that contributed to the production of the results for the 2016 PNWCA.  The primary result of the increased effort was that it was determined that the wetland area in the PNW and in its associated ecoregions are generally in poor condition.  The most likely cause is the high presence of Nonnative Plants.  It is hoped that the PNWCA provides a template for States and Tribes who have an interest in further understanding the differences in wetland condition between their ecoregions and/or other areas of concern.

Citation

Thiesing, M., M. Kentula, AND K. Blocksom. Report on the 2016 Pacific Northwest Wetland Condition Assessment. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-23/184, 2024.

• KENTULA-PNWCA REPORT-508 COMPLIANT.PDF (PDF)  (NA  pp, 6.8 MB, about PDF)